Effects of compressive and tensile stress on the growth mode of epitaxial oxide films

Oxide films were deposited on different substrates by laser molecular beam epitaxy. Reflection high-energy electron diffraction was performed to in situ investigate the change of growth mode and the lattice relaxation during the growth. An asymmetrical phenomenon was found in the two kinds of strain states, compressive stress and tensile stress of heterostructures with different lattice mismatch. In the case of BaTiO₃/SrTiO₃ (2.2%), 2D layer-by-layer growth mode without lattice relaxation can be maintained for a longer period for BTO films on STO with compressive stress, comparing to STO films on BTO with tensile stress. When MgO films were deposited on SrTiO₃ with a large mismatch of 7.8%, compressive stress leads to rapid lattice relaxation with a very thin wet layer, and 3D strained island were observed. As a comparison, SrTiO₃ films on MgO with tensile stress were configured. No RHEED patterns can be observed duo to a large tensile stress.     

Permeable reactive barrier for groundwater remediation

This article aims to provide an overview of the upcoming technology of permeable reactive barriers for groundwater remediation. A comprehensive list of references and web-links are also provided for further in-depth understanding. A brief discussion on the Australian perspective on this emerging technology is also included.     

Study of medium-cement concrete based on mixed Chamotte-periclase chromite filler

The possibility is demonstrated of using an addition of periclase-chromite filler (PCF) prepared from PCF grade broken material articles in medium-cement concrete with chamotte filler. The effect of this addition on cement hardening duration, strength and heat resistance is considered. Translated from Novye Ogneupory, No. 8, pp. 42–46, August 2008.     

A Low-Supply-Voltage CMOS Sub-Bandgap Reference

A low-power (21 $muhbox{W}$ ) bandgap reference source that is operable from a nominal supply voltage of 1.4 V is described. The circuit provides an output voltage equal to the bandgap voltage having a low output resistance and allows resistive loading. It does not use resistors or operational amplifiers. Thus, the design is suitable for fabrication in any digital CMOS technology. The circuit uses a current conveyor and current mirrors to convert the proportional to absolute temperature voltage into a current using a MOSFET. The current is converted back to a voltage by using the functional inverse of the FET $v-i$ characteristics. This makes the voltage gain linear and temperature independent. The absence of back-gate bias is the reason for achieving the low supply voltage of operation. Simulation results using the transistor models for the 0.18-$mu$m TSMC process show that the voltage-variation over the temperature range 0 to 100 $^{circ} {hbox {C}}$ is $≪$1 mV.      

Cost-Efficient SHA Hardware Accelerators

This paper presents a new set of techniques for hardware implementations of Secure Hash Algorithm (SHA) hash functions. These techniques consist mostly in operation rescheduling and hardware reutilization, therefore, significantly decreasing the critical path and required area. Throughputs from 1.3 Gbit/s to 1.8 Gbit/s were obtained for the SHA implementations on a Xilinx VIRTEX II Pro. Compared to commercial cores and previously published research, these figures correspond to an improvement in throughput/slice in the range of 29% to 59% for SHA-1 and 54% to 100% for SHA-2. Experimental results on hybrid hardware/software implementations of the SHA cores, have shown speedups up to 150 times for the proposed cores, compared to pure software implementations.      

Photo-Fenton removal of water-soluble polymers

This paper presents the results of experiments carried out in a laboratory-scale photochemical reactor on the photodegradation of different polymers in aqueous solutions by the photo-Fenton process. Solutions of three polymers, polyethyleneglicol (PEG), polyacrylamide (PAM), and polyvinylpyrrolidone (PVP), were tested under different conditions. The reaction progress was evaluated by sampling and analyzing the total organic carbon concentration in solution (TOC) along the reaction time. The behavior of the different polymers is discussed, based on the evolution of the TOC–time curves. Under specific reaction conditions, the formation and coalescence of solid particles was visually observed. Solids formation occurred simultaneously to a sharp decrease in the TOC of the liquid phase. This may be favorable for the treatment of industrial wastewater containing polymers, since the photodegradation process can be coupled with solid separation systems, which may reduce the treatment cost.     

Implementation of adaptive critic-based neurocontrollers for turbogenerators in a multimachine power system

This paper presents the design and practical hardware implementation of optimal neurocontrollers that replace the conventional automatic voltage regulator (AVR) and the turbine governor of turbogenerators on multimachine power systems. The neurocontroller design uses a powerful technique of the adaptive critic design (ACD) family called dual heuristic programming (DHP). The DHP neurocontrollers' training and testing are implemented on the Innovative Integration M67 card consisting of the TMS320C6701 processor. The measured results show that the DHP neurocontrollers are robust and their performance does not degrade unlike the conventional controllers even when a power system stabilizer (PSS) is included, for changes in system operating conditions and configurations. This paper also shows that it is possible to design and implement optimal neurocontrollers for multiple turbogenerators in real time, without having to do continually online training of the neural networks, thus avoiding risks of instability.     

Distributed Transmit Antenna Selection (DTAS) Under Performance or Energy Consumption Constraints

Motivated by the transmit antenna selection (TAS) concept, used in Multiple-Input-Multiple-Output systems, we argue for distributed transmit antenna selection (DTAS), which corresponds to a method of selecting a subset of available relays in cooperative diversity systems. Assuming amplify and forward relays, the proposed selection method represents a low-complexity tool for determining the optimum relaying set. Two optimization problems are studied: the error probability minimization subject to total energy consumption constraints, and the dual one, the total energy consumption minimization under error performance constraints. Numerical examples verify the advantage of the proposed method in adapting the number of relaying terminals to the desired performance-consumption tradeoff.     

Laminar-turbulent transition in an electromagnetically levitated droplet

During experiments on the MSL-1 (first microgravity science laboratory) mission of the space shuttle (STS-83 and STS-94, April and July 1997), a droplet of palladium-silicon alloy was electromagnetically levitated for viscosity measurements. For the nondeforming droplet, the resultant magnetohydrodynamic (MHD) flow inside the drop can be inferred from motion of impurity particulates on the surface. In the experiments, subsequent to melting, Joule heating produces a continuous reduction of viscosity of the fluid resulting in an acceleration of the flow with time. These observations indicate formation of a pair of co-rotating toroidal flow structures inside the spheroidal drop that undergo flow instabilities. As the fluid temperature rises, the amplitude of the secondary flow increases, and beyond a point, the tracers exhibit noncoherent chaotic motion signifying emergence of turbulence inside the drop. Assuming that the observed laminar-turbulent transition is shear-layer type, the internal structure of the toroidal loops is used to develop a semiempirical correlation for the onset of turbulence. Our calculations indicate that the suggested correlation is in modest agreement with the experimental data, with the transition occurring at a Reynolds number of 600.